192
Two-Stroke Engines
Copyright Goodheart-Willcox Co., Inc.
element is loose. See if the element was installed
correctly. Also, if the air filter element was com-
pletely obstructed, the normal operation of a
running engine could begin pulling in contam-
inants through the filter element itself, creating
a very fine dusting of debris on the clean air sur-
faces. Also, do not overlook the obvious: Was the
operator running the engine without the air fil-
ter element?
Check the choke system once the air filter ele-
ment has been removed. If the choke is mounted
on the air filter backing plate, make sure it
closes easily without hanging up. If the choke is
set and released remotely, verify that it is closed
completely in the full-choke position and that it
opens completely in the full-off position.
Ignition System
Depending on the engine manufacturer, the
spark plug boot, connector, high-tension lead,
and spark plug may not be immediately visible.
Some engine covers may need to be removed to
inspect one or more of these components.
WARNING
The ignition system can produce from 10,000
to 40,000 volts. Use extreme caution when
working on or around the ignition system.
Inspect the spark plug boot for cracks or dete-
rioration. The rubber should be pliable. The
connector should firmly snap and hold onto the
spark plug terminal. Sometimes, the metal ter-
minal connector has become pulled out or dis-
connected from the high-tension lead.
“Did the engine have spark in its existing
condition?” A spark test was conducted during ”
the troubleshooting phase of diagnosis. If the
test indicated that there was no spark, a more
detailed inspection of the ignition system is
needed. If the test revealed that spark was being
generated, the next step is to determine if the
spark is continuous or intermittent.
“Is there an intermittent spark?” If the ”
engine ran and continued to run during the
spark test, check for an intermittent spark. The
only way to determine if the ignition is produc-
ing an intermittent spark is to run the engine
with the spark tester installed. This test should
be performed with the unit completely intact,
with fuel in the tank and the correct attach-
ments installed. If this test is performed on a
chain saw, the bar and chain must be correct for
the chain saw being tested. The chain must be
sharp and adjusted correctly.
“Is there an intermittent spark when the
engine is cold and idling, and cold at WOT?”
Run the engine at idle for 10 seconds and observe
the spark tester. Increase engine speed to WOT
for 10 seconds and observe the spark tester.
Reduce the engine speed to idle. Note any inter-
ruptions in spark.
“Is there an intermittent spark at idle
and WOT when the engine is hot?” Continue ”
increasing and decreasing between idle and
WOT for three minutes. This brings the engine
up to operating temperature. Observe the spark
tester at idle and at WOT. Note any interrup-
tions in spark.
“Is there an intermittent spark when the
engine is hot and under a load?” (This applies ”
to chain saws only.) Perform a cut at WOT for
about 10 seconds and observe the spark tester
during the cut.
WARNING
Do not operate a chain saw at WOT without a
load for more than 10 seconds. This can cause
serious damage to the engine.
No debris Clean behind air filter
Goodheart-Willcox Publisher
Figure 9-19. If the air filter element is doing its
job, the surface of the air filter backing plate and
the throat of the carburetor should be completely
clean.